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Predicting human thermal comfort and safety requires quantitative knowledge of the convective heat transfer between the body and its surrounding. So far, convective heat transfer coefficient correlations have been based only upon measurements or simulations of the average body shape of an adult. To address this knowledge gap, here we quantify the impact of adult human body shape on forced convection. To do this, we generated fifty three-dimensional human body meshes covering 1st to 99th percentile variation in height and body mass index (BMI) of the USA adult population. We developed a coupled turbulent flow and convective heat transfer simulation and benchmarked it in the 0.5 to 2.5 m·s−1 air speed range against prior literature. We computed the overall heat transfer coefficients, hoverall, for the manikins for representative airflow with 2 m·s−1 uniform speed and 5% turbulence intensity. We found that hoverall varied only between 19.9 and 23.2 W·m−2 K−1. Within this small range, the height of the manikins had negligible impact while an increase in the BMI led to a nearly linear decrease of the hoverall. Evaluation of the local coefficients revealed that those also nearly linearly decreased with BMI, which correlated to an inversely proportional local area (i.e., cross-sectional dimension) increase. Since even the most considerable difference that exists between 1st and 99th percentile BMI manikins is less than 15% of hoverall of the average manikin, it can be concluded that the impact of the human body shape on the convective heat transfer is minor.

In the present paper, along with experimental study, CFD analysis of forced convection in a twisted tube is performed, using the transition SST model which can predict the change of flow regime from laminar through transition to turbulent. The differential governing equations are discretized by the finite volume method. The investigations are conducted for Reynolds numbers ranging from 100 to 50000 covering laminar, transitional and turbulent regimes, and for three length and three pitch ratios. The predictions are observed to show a good agreement with the measurements and published correlations of other authors. The analysis indicates that the large length ratio and small pitch ratio yields a higher heat transfer rate with relatively low performance penalty. The transition from laminar to turbulent regime is observed between Reynolds numbers of 2500 to 3500 for all cases. For almost all investigated cases the performance factors are greater than unity. nema

Solar energy is a ubiquitous renewable resource for photovoltaic (PV) power generation; however, higher operating temperatures significantly reduce the efficiency of PV modules, impacting their electrical output and increasing the levelized cost of energy (LCOE). This study aims to enhance conventional PV systems’ electrical efficiency and annual energy recovery while reducing the LCOE through thermal management using microchannel heat sinks (MCHSs) under forced convection. A 600 W monocrystalline PV module was analyzed, recognizing an efficiency reduction of ~20% under actual operating conditions due to thermal effects, with the surface temperature reaching up to 63.76°C without cooling. In addition, analytical calculations were used to determine an incident solar irradiance of 957.33 W/m 2 for an industrial location in Lahore, Pakistan. Similarly, computational fluid dynamics (CFDs) simulations were conducted using single and dual‐layer MCHSs configurations with water as the coolant at inlet velocities ranging from 0.01 to 1.0 m/s. The dual‐layer MCHSs significantly reduced the PV module’s surface temperature from 63.76 to ~25.65°C at an inlet velocity of 1.0 m/s, achieving a temperature reduction of 38.11°C. This thermal management increased the electrical efficiency from 18.33% (without cooling) to 22.27%, an efficiency gain of ~4%. The annual energy recovery improved substantially; at 1.0 m/s, the dual‐layer configuration increased the annual energy output by 227,954 kWh/year (about 21.89%) compared to the no‐cooling scenario, reaching 1,269,131 kWh/year. Furthermore, the LCOE was reduced to as low as 6.27 PKR/kWh over a 30‐year operational lifespan at lower velocities, demonstrating improved cost‐effectiveness. Meanwhile, optimal velocity was identified between 0.2 and 0.5 m/s, balancing thermal performance and economic viability. Finally, this study concludes that thermal management using dual‐layer MCHSs effectively enhances PV module efficiency, increases annual energy recovery, and reduces LCOE, contributing to sustainable and economical solar energy integration in industrial applications.

In this work, flow boiling heat transfer coefficients of deionized water and copper oxide water-based nanofluids at different operating conditions have been experimentally measured and compared. The liquid flowed in an annular space. According to the experiments, two distinguished heat transfer regions with two different mechanisms can be seen namely forced convective and nucleate boiling regions. Results demonstrated that with increasing the applied heat flux, flow boiling heat transfer coefficient increases for both of test fluids at both heat transfer regions. In addition to, by increasing the flow rate of fluid, the heat transfer coefficient dramatically increases at both regions. Influence of inlet temperature of fluid to the annulus as a complicated parameter has been investigated and briefly discussed. Results showed that inlet temperature of fluid displaces the boundary between forced convection and nucleate boiling areas such that with increasing the inlet temperature, nucleation mechanism become dominant mechanism at lower heat fluxes. Furthermore, higher heat transfer coefficient can be obtained due to interactions of bubbles and local agitations. Also, Chen type model was modified in terms of thermo-physical properties and examined to experimental data. Results showed that experimental data are in a good agreement with those of obtained by the correlation with deviation up to 30%.

A local thermal non-equilibrium analysis of heat and fluid flow in a channel fully filled with aluminum foam is performed for three cases: (a) pore density of 5 PPI (pore per inch), (b) pore density of 40 PPI, and (c) two different layers of 5 and 40 PPI. The dimensionless forms of fully developed heat and fluid flow equations for the fluid phase and heat conduction equation for the solid phase are solved analytically. The effects of interfacial heat transfer coefficient and thermal dispersion conductivity are considered. Analytical expressions for temperature profile of solid and fluid phases, and also the channel Nusselt number (NuH) are obtained. The obtained results are discussed in terms of the channel-based Reynolds number (ReH) changing from 10 to 2000, and thickness ratio between the channel height and sublayers. The Nusselt number of the channel with 40 PPI is always greater than that of the 5 PPI channel. It is also greater than the channel with two-layer aluminum foams until a specific Reynolds number then the Nusselt number of the channel with two-layer aluminum foams becomes greater than the uniform channels due to the higher velocity in the outer region and considerable increase in thermal dispersion.

During friction surfacing of dissimilar alloys, different shielding techniques are used to avoid oxidation and corrosion behaviour of developed coatings. The present study explores the effect mechanical and corrosion performance of friction surfaced aluminium deposits over carbon steel by forced convection nitrogen shielding (FCNS) process. Appropriate friction surfacing process parameters are selected for experimental work, and the substrate plate was maintained a constant preheating temperature of 200 °C for obtaining better deposition. During deposition process, three different volume flow rates of nitrogen gas were supplied, namely FCNS-5, FCNS-10, and FCNS-15. The developed coating’s mechanical strength and corrosion behaviour are intensively investigated and compared with the coating developed by without apply of forced convention process (FCNS-0). The microstructural image received from electron backscattered diffraction (EBSD shows that the restoration activities and dynamically recrystallized grain growth are high towards higher volume of nitrogen supplied during FCNS process; as a result, an improved mechanical strength of the coating was achieved. Furthermore, the corrosion behaviour was analysed by electrochemical impedance and potentiodynamic polarization test. The impedance test shows a less corrosion current of the aluminium coating at FCNS-15 process. The potential dynamic polarization test confirms a lesser I corr and higher E corr value of aluminium coating in FCNS-15 process which proved a better corrosion resistance deposition compared to other processes.

Based on preliminary investigations under controlled condition of drying experiments, a mixed-mode solar dryer with forced convection using smooth and rough plate solar collector was constructed. This paper describes the development of dryer considerations followed by the results of experiments to compare the performance of the smooth and the roughed plate collector. The thermal performance of solar collector was found to be poorer because of low convective heat transfer from the absorber plate to air. Artificial rib roughness on the underside of the absorber plate has been found to considerably enhance the heat transfer coefficient. The absorber plate of the dryer attained a temperature of 69.2°C when it was studied under no-load conditions. The maximum air temperature in the dryer, under this condition, was 64.1°C. The dryer was loaded with 3 kg of grapes having an initial moisture content of 81.4%, and the final desired moisture content of 18.6% was achieved within 4 days while it was 8 days for open sun drying. This prototype dryer was designed and constructed to have a maximum collector area of 1.03 m 2 . This solar dryer been be used in experimental drying tests under various loading conditions.

This paper numerically investigates the heat transfer performance of thermally developing non-Darcy forced convection in a fluid-saturated porous medium tube under asymmetric entrance temperature boundary conditions. The Brinkman flow model and the local thermal non-equilibrium (LTNE) model are employed to establish the mathematical model of the studied problem to predict the forced convective heat transfer. Then, the mathematical model is numerically solved using COMSOL Multiphysics. Consequently, the fluid velocity field, the solid temperature field, the fluid temperature field and the Nusselt number are obtained. Moreover, the dependences of the Nusselt number on some key parameters are analyzed in detail. The results show that the distribution characteristics of the Nusselt number are strongly dependent on the form of the entrance temperature function. Meanwhile, it is found that the Nusselt number increases first and then tends to approach an asymptotic value with the increase in the Darcy number and the Biot number. The Nusselt number monotonously increases with increasing the Péclet number. On the contrary, the Nusselt number decreases first and then tends to be an asymptotic value owing to the increase in the thermal conductivity ratio and the viscosity ratio. This study is of benefit to provide in-depth insights into the non-Darcy forced convective heat transfer in porous tubes with asymmetric inlet temperature under LTNE condition.

Combined free and forced convection Couette-Hartmann flow of a viscous, incompressible and electrically conducting fluid in rotating channel with arbitrary conducting walls in the presence of Hall current is investigated. Boundary conditions for magnetic field and expressions for shear stresses at the walls and mass flow rate are derived. Asymptotic analysis of solution for large values of rotation and magnetic parameters is performed to highlight nature of modified Ekmann and Hartmann boundary layers. Numerical solution of non-linear energy equation and rate of heat transfer at the walls are computed with the help of MATHEMATICA. It is found that velocity depends on wall conductance ratio of moving wall and on the sum of wall conductance ratios of both the walls of channel. There arises reverse flow in the secondary flow direction near central region of the channel due to thermal buoyancy force. Thermal buoyancy force, rotation, Hall current and wall conductance ratios resist primary fluid velocity whereas thermal buoyancy force and Hall current favor secondary fluid velocity in the region near lower wall of the channel. Magnetic field favors both the primary and secondary fluid velocities in the region near lower wall of the channel.

Purpose>This work aims to study the hydrothermal behavior of mortar cement toward certain environmental factors (ambient air temperature and air velocity) based on its drying kinetics data. The objective is to provide a better understanding and controlling the stability of mortar structures, which integrate the sorption phenomenon, drying process, air pressure and intrinsic characteristics. This leads to predict the comportment of mortar structures in relation with main environmental factors and minimize the risk of cracking mortar structures at an early age.Design/methodology/approach>Thermokinetic study was carried out in natural and forced convection solar drying at three temperatures 20, 30 and 40°C and three air velocities (1, 3 and 5 m.s-1). The empirical and semiempirical models tested successfully describe the drying kinetics of mortar. These models simulate the drying process of water absorbed by capillarity, which is the most common humidity transfer mechanism in building materials and contain parameters with physical significance, which integrate the effect of several environmental factors and intrinsic characteristics of mortar structures.Findings>The models simulate the drying process of water absorbed by capillarity, which is the most common humidity transfer mechanism in building materials and contain parameters with physical significance, which integrate the effect of several environmental factors and intrinsic characteristics of mortar structures. The average activation energy obtained expressed the temperature effect on the mortar diffusivity. The drying constant and the diffusion coefficient can be used to predict the influence of these environmental factors on the drying behavior of various building materials and therefore on their durability.Originality/value>Evaluation of the effect of several environmental factors and intrinsic characteristics of mortar structures on their durability.